Which from the following defines enthalpy of a system?

Which of the following symbols represent heat of reaction at constant volume?

Calculate the entropy change for melting 1 g ice at $0^{\circ} \mathrm{C}$ in $\mathrm{Jg}^{-1} \mathrm{~K}^{-1}$ if heat of fusion of ice at $0^{\circ} \mathrm{C}$ is $80 \mathrm{~J} \mathrm{~K}^{-1}$.

Which of the following set of properties is correct when one mole of a gas is heated keeping volume constant by increasing temperature and supplying 500 J of heat?